I'm in the middle of setting up an Exchange 2010 Server. Currently, we use a SaaS provider for Exchange 2007 services. Some (but not all) of my users have been reporting that they are receiving Outlook/Exchange login prompts to login to the new Exchange server. This is happening without any intervention on the client's machines. The Exchange server is a member of the domain and connects to the domain site remotely through a site-to-site VPN. What can I do to prevent these login prompts from appearing? Will shutting down the new server until it is time to switch resolve these issues?
A little more info: I found that on one of the client computers, all of the settings for Outlook over HTTP had been changed (automatically) from webmail.provider.com to mail.company.com (the latter being the new server). This happened when I enabled Outlook Anywhere access on Exchange 2010. I changed the client's settings back, and everything was groovy. But, when I disabled Outlook Anywhere again, the logon prompt came back.
Best Answer
When Outlook starts up it looks for the Exchange SCP (service connection point) in AD which directs Outlook to the Autodiscover URL of the Exchange Server, which stores the Exchange client access settings in the Autodiscover.xml file. That's why Outlook automatically configures itself to connect to the internal Exchange server. I dealt with this during an SBS migration while we staged and scheduled the transition from an external email provider to Exchange, with the Exchange migration occurring after the migration from SBS 2003 to SBS 2007. Here's how we dealt with it:
We configured the MSExchangeAutodiscoverAppPool application pool on the Exchange server to not start automatically. The MSExchangeAutodiscoverAppPool application pool is used by the Autodiscover virtual directory on the Exchange server to perform the functions listed above (Outlook automatic configuration). With the application pool stopped, you're essentially disabling Autodiscover. You can re-enable it when you're ready by setting the application pool back to automatic startup.
http://technet.microsoft.com/en-us/library/bb124251.aspx
http://www.msexchange.org/articles_tutorials/exchange-server-2010/management-administration/exchange-autodiscover.html